Purpose: The aim of this study was to describe the recent conditions associated with implantable defibrillation therapy for individual underlying heart diseases.
Methods: Ten thousand six hundred and five patients with implantable cardioverter-defibrillators (ICDs) or cardiac resynchronization therapy defibrillators (CRT-Ds) that were implanted from 2006 to 2010 were selected from the Japan Cardiac Device Therapy Registry database. They were divided into 12 disease categories and further divided into either primary or secondary prevention of sudden cardiac death.
Results: The major underlying diseases of the patients in this cohort were ischemic heart disease (IHD, 35%), dilated cardiomyopathy (DCM, 25%), hypertrophic cardiomyopathy (HCM, 8%), and Brugada syndrome (Brugada, 8%). There were no structural heart diseases in this cohort; the incidence of IHD was relatively lower than that of western countries, while the incidence of cardiomyopathy was higher. The percentage of primary prevention (% primary) among the individual diseases varied. IHD was the most prevalent underlying condition in the patient cohort; however, the % primary was 33%, which was relatively lower than that of the other structural heart diseases. The % primary was relatively higher in patients with DCM (57%) and Brugada (47%). Over 5 years, the % primary gradually increased in patients with DCM, IHD, and HCM, with a particularly dramatic increase in those with DCM. A decrease in the % primary among patients with Brugada began in 2008.
Conclusions: In patients that underwent implantable defibrillation therapy, there was a relatively lower % primary in the IHD group, and a substantial increase in the % primary in patients with DCM.

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In this study, the prevalence and prognostic significance of the early repolarization (ER) pattern in the inferolateral leads in patients with Brugada syndrome were investigated. Clinical, genetic, and electrophysiological data were collected and analyzed from 69 individuals with either a spontaneous or drug-induced Brugada type 1 electrocardiogram (ECG) pattern. An ER pattern was defined as J-point elevation at least 0.1 mV from the baseline in at least 2 inferior or lateral leads. The presence of late potentials and inducibility of ventricular fibrillation (VF) by programmed stimulation were compared between patients with and without a J wave. Follow-up data, including outcome events, were obtained for all patients. An ER pattern was observed in the inferolateral leads in 6 patients with a spontaneous Brugada type 1 ECG pattern and in 1 patient with a drug-induced Brugada type 1 ECG pattern. There was no significant intergroup difference in symptoms, family history of sudden cardiac death, prevalence of late potentials, or inducibility of VF. No patient with the ER pattern developed a cardiac event during the mean follow-up period of 73.6±38.1 months. The ER pattern in the inferolateral leads is not uncommon in Brugada syndrome; however, the presence of a J wave does not appear to be associated with subsequent arrhythmic events in patients with Brugada syndrome.

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An understanding of the clinical aspects of electrical storm (E-storms) in patients with implantable cardiac shock devices (ICSDs: ICDs or cardiac resynchronization therapy with defibrillator [CRT-D]) may provide important information for clinical management of patients with ICSDs. The Nippon Storm Study was organized by the Japanese Heart Rhythm Society (JHRS) and Japanese Society of Electrocardiology and was designed to prospectively collect a variety of data from patients with ICSDs, with a focus on the incidence of E-storms and clinical conditions for the occurrence of an E-storm. Forty main ICSD centers in Japan are participating in the present study. From 2002, the JHRS began to collect ICSD patient data using website registration (termed Japanese cardiac defibrillator therapy registration, or JCDTR). This investigation aims to collect data on and investigate the general parameters of patients with ICSDs, such as clinical backgrounds of the patients, purposes of implantation, complications during the implantation procedure, and incidence of appropriate and inappropriate therapies from the ICSD. The Nippon Storm Study was planned as a sub-study of the JCDTR with focus on E-storms. We aim to achieve registration of more than 1000 ICSD patients and complete follow-up data collection, with the assumption of a 5–10% incidence of E-storms during the 2-year follow-up.

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A 68-year-old man with dilated cardiomyopathy (left ventricular ejection fraction, 15%) and nonsustained ventricular tachycardia received an implantable cardioverter defibrillator. Even though his cardiac status had greatly improved 2 years later after β-blocker therapy, he experienced 2 episodes of sudden shock when he was squatting in a bathroom without any preceding symptoms. His serum electrolyte and plasma glucose levels were normal. Interrogation of the device revealed that the shock was caused by sinus tachycardia and T-wave oversensing. A number of episodes of nonsustained ventricular tachycardia due to T-wave oversensing was also recorded. Follow-up interrogation of the device with the patient in the supine position could not reproduce the T-wave oversensing. We were able to elicit T-wave oversensing only after reproduction of the patient's clinical situation using isoproterenol and postural changes (i.e., sinus tachycardia and squatting). This case suggests that sudden increases in nonsustained ventricular tachycardia events may be caused by T-wave oversensing, and postural changes should be taken into consideration in such situations.

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AT caused by SVC fibrillation: Here, we report a case of a 62-year-old man with a history of incessant atrial tachycardia (AT) for several years. An electrophysiological study revealed rapid and irregular activity in the superior vena cava (SVC), but the surface 12-lead electrocardiogram (ECG) exhibited a relatively regular AT (atrial cycle length=240 ms). CARTO mapping of the right atrium (RA) demonstrated that the earliest atrial activation occurred at the posterior septum of the upper RA (the SVC–RA junction). Intravenous administration of 20 mg adenosine triphosphate (ATP) led to an acceleration of the SVC–RA conduction up to 1:1 conduction, and the atrial cycle length decreased, consequently converting the AT to transient atrial fibrillation (AF). Application of single radiofrequency energy at the earliest atrial activation site during tachycardia terminated the AT and achieved isolation of the SVC from the RA, despite the continued presence of fibrillation in the SVC. We speculated that SVC fibrillation with spontaneous conduction block at the SVC–RA junction was the cause of this AT.

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We report a rare case of atrial oversensing by a VVI pacemaker that caused ventricular asystole. Changing the programming to VVT mode not only eliminated the problem but also provided atrioventricular synchrony and rate responsiveness.

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In recent years, the need for a lead-removal technique has increased. Various extraction devices for traction and dissection are used worldwide, and quite a few of these devices are available in Japan. This paper details our experience using a new tool for manual dissection during transvenous pacing lead extraction. Five leads from 4 patients were considered for extraction using a new tool, the Amplatz renal dilator (Cook Ireland Ltd., Limerick, Ireland). The dilator was advanced following the lead course, similar to the over-the-wire technique. From 2 (50%) of the patients, 2 leads were extracted successfully using this procedure. No complications occurred in any of the patients. The remaining 3 leads could not be removed due to 2 reasons: first, the lead was entrapped in the supra vena cava, and second, the new dissection tool could not be inserted into the implant vein because of the tight space under the clavicle. Although the Amplatz renal dilator was useful for dissection, it was not sufficient for achieving complete procedural success. Our experience suggests that the Amplatz renal dilator can be a feasible and safe option for low-risk manual dissection in transvenous pacing lead extraction.

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The phenomenon of a 2:1 bundle branch block is reported during atrioventricular (AV) nodal reentrant tachycardia, sinus tachycardia, atrial fibrillation, and atrial flutter. A 2:1 bundle branch block is attributed to first- and second-degree bundle branch block, linking, electrical alternans, aberrancy, or supernormal conduction. However, the same phenomenon has not been reported in AV reentrant tachycardia. Herein, we report the case of a 52-year-old man presenting with orthodromic atrioventricular reentrant tachycardia with a 2:1 right bundle branch block.

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A 67-year-old man with poor left ventricular function due to a dilated cardiomyopathy was implanted with an implantable cardioverter defibrillator for secondary prevention. Eight years later, he was admitted to our hospital with worsening of heart failure. An electrocardiogram showed a repetitive nonreentrant ventriculoatrial synchrony (RNRVAS). RNRVAS is a device-related arrhythmia that can occur when a dual-chamber pacemaker does not sense a retrograde P wave within the postventricular atrial refractory period, resulting in a repetitive ventricular pacing and noncaptured atrial pacing after the retrograde P wave. We suspected that ventricular pacing caused his heart failure and used the noncompetitive atrial pacing algorithm, which was programmed to prevent RNRVAS. The algorithm was able to prevent the arrhythmia, and the patient successfully recovered from heart failure.

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We report on a 64-year-old female patient who underwent cardiac surgery for left atrial myxoma, using the superior septal approach with large atrial septal wall resection and patch closure. The superior septal approach is reported to be a relatively safe method for preventing the development of sinus node dysfunction after cardiac surgery. However, this patient developed sinus node dysfunction after surgery and required the implantation of a permanent pacemaker. Moreover, in this case, determining the appropriate positions of the pacemaker leads was difficult because of the presence of a large conduction delay in the interatrium. Selecting the appropriate atrioventricular delay settings was important in order to achieve proper sequential contractions between the left atrium and the left ventricle.

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Here, we report a case of a 69-year-old patient with paroxysmal atrial fibrillation and inducible typical atrial flutter who required catheter ablation. After pulmonary vein isolation, cavotricuspid isthmus ablation was performed. During ablation at a lateral site of the cavotricuspid isthmus, a spiky potential appeared at the distal electrode of the ablation catheter, and subsequently, a 2:1 atrioventricular (AV) block occurred. Radiofrequency (RF) delivery at the same site caused a similar phenomenon, implying that the spiky potential may reflect a slow pathway potential as an anatomical variant of the rightward extension of the AV node.

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